Add region(::Plan) for accessing transformed region

Project.toml

@@ -1,6 +1,6 @@
 name = "AbstractFFTs"
 uuid = "621f4979-c628-5d54-868e-fcf4e3e8185c"
-version = "1.1.0"
+version = "1.2.0"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

README.md

@@ -23,7 +23,7 @@ To define a new FFT implementation in your own module, you should
   inverse plan.
 
 * Define a new method `AbstractFFTs.plan_fft(x, region; kws...)` that returns a `MyPlan` for at least some types of
-  `x` and some set of dimensions `region`.
+  `x` and some set of dimensions `region`.   The `region` (or a copy thereof) should be accessible via `fftdims(p::MyPlan)` (which defaults to `p.region`).
 
 * Define a method of `LinearAlgebra.mul!(y, p::MyPlan, x)` (or `A_mul_B!(y, p::MyPlan, x)` on Julia prior to
   0.7.0-DEV.3204) that computes the transform `p` of `x` and stores the result in `y`.

docs/src/api.md

@@ -19,6 +19,7 @@ AbstractFFTs.brfft
 AbstractFFTs.plan_rfft
 AbstractFFTs.plan_brfft
 AbstractFFTs.plan_irfft
+AbstractFFTs.fftdims
 AbstractFFTs.fftshift
 AbstractFFTs.ifftshift
 AbstractFFTs.fftfreq

src/AbstractFFTs.jl

@@ -5,7 +5,7 @@ import ChainRulesCore
 export fft, ifft, bfft, fft!, ifft!, bfft!,
        plan_fft, plan_ifft, plan_bfft, plan_fft!, plan_ifft!, plan_bfft!,
        rfft, irfft, brfft, plan_rfft, plan_irfft, plan_brfft,
-       fftshift, ifftshift, fftshift!, ifftshift!, Frequencies, fftfreq, rfftfreq
+       fftdims, fftshift, ifftshift, fftshift!, ifftshift!, Frequencies, fftfreq, rfftfreq
 
 include("definitions.jl")
 include("chainrules.jl")

src/definitions.jl

@@ -15,6 +15,18 @@ size(p::Plan, d) = size(p)[d]
 ndims(p::Plan) = length(size(p))
 length(p::Plan) = prod(size(p))::Int
 
+"""
+    fftdims(p::Plan)
+
+Return an iterable of the dimensions that are transformed by the FFT plan `p`.
+
+# Implementation
+
+For legacy reasons, the default definition of `fftdims` returns `p.region`.
+Hence this method should be implemented only for `Plan` subtypes that do not store the transformed dimensions in a field named `region`.
+"""
+fftdims(p::Plan) = p.region
+
 fftfloat(x) = _fftfloat(float(x))
 _fftfloat(::Type{T}) where {T<:BlasReal} = T
 _fftfloat(::Type{Float16}) = Float32
@@ -243,6 +255,8 @@ ScaledPlan(p::ScaledPlan, α::Number) = ScaledPlan(p.p, p.scale * α)
 
 size(p::ScaledPlan) = size(p.p)
 
+fftdims(p::ScaledPlan) = fftdims(p.p)
+
 show(io::IO, p::ScaledPlan) = print(io, p.scale, " * ", p.p)
 summary(p::ScaledPlan) = string(p.scale, " * ", summary(p.p))
 

test/runtests.jl

@@ -60,18 +60,21 @@ end
         @test eltype(P) === ComplexF64
         @test P * x ≈ fftw_fft
         @test P \ (P * x) ≈ x
+        @test fftdims(P) == dims
 
         fftw_bfft = complex.(size(x, dims) .* x)
         @test AbstractFFTs.bfft(y, dims) ≈ fftw_bfft
         P = plan_bfft(x, dims)
         @test P * y ≈ fftw_bfft
         @test P \ (P * y) ≈ y
+        @test fftdims(P) == dims
 
         fftw_ifft = complex.(x)
         @test AbstractFFTs.ifft(y, dims) ≈ fftw_ifft
         P = plan_ifft(x, dims)
         @test P * y ≈ fftw_ifft
         @test P \ (P * y) ≈ y
+        @test fftdims(P) == dims
 
         # real FFT
         fftw_rfft = fftw_fft[
@@ -84,18 +87,21 @@ end
         @test eltype(P) === Int
         @test P * x ≈ fftw_rfft
         @test P \ (P * x) ≈ x
+        @test fftdims(P) == dims
 
         fftw_brfft = complex.(size(x, dims) .* x)
         @test AbstractFFTs.brfft(ry, size(x, dims), dims) ≈ fftw_brfft
         P = plan_brfft(ry, size(x, dims), dims)
         @test P * ry ≈ fftw_brfft
         @test P \ (P * ry) ≈ ry
-
+        @test fftdims(P) == dims
+
         fftw_irfft = complex.(x)
         @test AbstractFFTs.irfft(ry, size(x, dims), dims) ≈ fftw_irfft
         P = plan_irfft(ry, size(x, dims), dims)
         @test P * ry ≈ fftw_irfft
         @test P \ (P * ry) ≈ ry
+        @test fftdims(P) == dims
     end
 end
 
@@ -187,7 +193,7 @@ end
     # normalization should be inferable even if region is only inferred as ::Any,
     # need to wrap in another function to test this (note that p.region::Any for
     # p::TestPlan)
-    f9(p::Plan{T}, sz) where {T} = AbstractFFTs.normalization(real(T), sz, p.region)
+    f9(p::Plan{T}, sz) where {T} = AbstractFFTs.normalization(real(T), sz, fftdims(p))
     @test @inferred(f9(plan_fft(zeros(10), 1), 10)) == 1/10
 end